Emerging conservation problems require immediate attention. Viral hemorrhagic septicemia, or VHS, is one such issue. This viral fish disease has recently caused major episodes of fish die-offs in the Great Lakes, including Lake Erie. Scores of game and non-game species died in droves in spring and early summer of 2006 in several waters in the Great Lakes. Large fish kills were reported in the U.S. and Canada. The disease is not transmitted to people.
To address this issue, the U.S. Fish & Wildlife Service’s Division of the National Fish Hatchery System convened an international body of fish health and fishery management experts in August to address VHS. They gathered at the Service’s Great Lakes-Big Rivers regional office in Minneapolis to share what is known about this new virus in the Great Lakes, and charted an immediate course to learn more and direct future fishery management needs and research.
A leading expert on VHS in the United States, Jim Winton of the US Geological Survey, indicated that the VHS virus exists in four strains, with a single, unique sub-strain occurring in the Great Lakes. The VHS
virus has been known in Europe, Japan, and the coasts of the U.S. for many years; how it came to occur in the Great Lakes is not known. Winton speculates that it may have originated in ballast water from ocean-going ships sailing into the Great Lakes, or that it may have hitchhiked in shipments of hatchery-raised fish. Though the virus’s origin remains unknown, Winton said that the virus’s lack of genetic diversity in the Great Lakes indicates that it probably has only recently arrived to Great Lakes waters.
The virus could move through the Great Lakes to new species of fish that so far have not shown vulnerability to the disease, and it could move to new waters. The virus will probably persist in low levels and some fish will carry the virus without disease symptoms, much like a person can carry a cold virus without actually catching a cold. But those carriers can spread it, which can be a problem in stemming the spread.
Scientists expect the disease to spread in the contiguous Great Lakes and possibly into tributary streams; more fish-kills are to be expected, but it could be that in time, further outbreaks will be attenuated as surviving fish exposed to the virus become immune. Further outbreaks of the disease may be less explosive than that which unfolded in early 2006.
Inoculating fish in the wild to prevent the spread of disease is simply impossible. From this Minneapolis meeting, the attending scientists determined there is much to be learned about VHS, both from a biological and environmental standpoint. They also determined that containment in the Great Lakes is paramount.
Recreational boaters and anglers should clean and disinfect their craft and gear much like they are already encouraged to do to stop hitchhiking aquatic nuisance species.
The full effect of this viral disease remains to be seen. But what is known is the economic impact from large die-offs of important game fishes like trophy muskellunge, smallmouth bass, and yellow perch in the Great Lakes region could be profound. Commercial fisheries are also likely to be harmed. Of the 12 known species impacted by the disease, only two species were not game fishes. The affects of VHS to endangered species conservation could be equally profound, all underscoring the immediacy of this conservation problem.
Robert Bakal, DVM, is the Aquatic Animal Health Coordinator, Division of the National Fish Hatchery System in Washington DC. He can be reached at [email protected] or call 919-513-6851By: Dr. Robert Bakal, US Fish & Wildlife Service
